Optically readable strip for analyte detection having on-strip orientation index

Abstract

A test strip is provided for determining the presence or quantity of an analyte in a liquid by inserting the strip into an optical reading apparatus. The test strip is provided with an orientation index zone having a reflectance that contrasts with the reflectance of areas contiguous thereto and such orientation index zone is employed to affirm that the test strip has not been inserted upside down with respect to the apparatus.

What is claimed is:  
     
       1. A test strip for determining the presence or quantity of an analyte in a liquid by inserting said test strip into an optical reading apparatus; said test strip comprising: 
       a portion, for having liquid applied thereto, said portion having an area on a major surface of the strip defining a reaction zone, such reaction zone varying in reflectance as a function of the quantity of analyte in the applied liquid;  
       said test strip further comprising an area on said major surface defining an orientation index zone, said orientation index zone being positioned to lead said reaction zone as said strip is inserted into said apparatus;  
       said orientation index zone having a contrasting reflectance relative to that of the areas of the major surface contiguous to the orientation index zone;  
       whereby said apparatus may be provided with optical means for sequentially determining reflectance values of the major surface as the strip is inserted into the apparatus and with microprocessing means for detecting the presence of the orientation index zone or for reporting its absence.  
     
     
       2. The strip of  claim 1  wherein said orientation index zone is positioned on said major surface to lead said contiguous area as the strip is to be inserted into said apparatus. 
     
     
       3. The strip of  claim 2  wherein the reflectance of said contiguous area is at least 1.5 times the reflectance of said orientation index zone. 
     
     
       4. The strip of  claim 3  wherein the reflectance of said contiguous area is at least two times the reflectance of said orientation index zone. 
     
     
       5. The strip of  claim 2  wherein the reflectance of said contiguous area is no more than about 0.67 times the reflectance of said orientation index zone. 
     
     
       6. The strip of  claim 5  wherein the reflectance of said contiguous area is no more than about 0.5 times the reflectance of said orientation index zone. 
     
     
       7. The strip of  claim 1  wherein the orientation index zone reflects no more than 0.9 times the light reflected when no strip is present in the apparatus. 
     
     
       8. The strip of  claim 7  wherein the orientation index zone reflects no more than 0.5 times the light reflected when no strip is present in the apparatus. 
     
     
       9. The strip of  claim 1  wherein the orientation index zone reflects at least 1.1 times the light reflected when no strip is present in the apparatus. 
     
     
       10. The strip of  claim 9  wherein the orientation index zone reflects at least two times the light reflected when no strip is present in the apparatus. 
     
     
       11. In a system for determining the presence or quantity of an analyte in a liquid applied to a test strip and inserted into an apparatus, a method for determining that the strip has been properly oriented in said apparatus, said method comprising: 
       inserting said strip into said apparatus, said strip comprising a portion having liquid applied thereto, said portion having an area on a major surface of said strip defining a reaction zone, said reaction zone varying in reflectance as a function of the quantity of analyte in the applied liquid and said strip further comprising an orientation index zone positioned to lead said strip as it is inserted into said apparatus, said orientation index zone having a contrasting reflectance relative to that of the area of the major surface contiguous to the orientation index zone;  
       determining the reflectance of the major surface of the strip by directing light at a fixed position in the pathway of the strip as it is inserted and detecting the reflected light;  
       detecting the presence or absence of reflected light corresponding to the passage of said orientation index zone past said fixed position as the strip is inserted into said passageway.